1. Field of the Invention
The present invention relates to a fuel cell system.
2. Discussion of the Background
Recently, a fuel cell has been developed which generates electric power by supplying hydrogen (fuel gas) and air (oxidant gas) containing oxygen. The fuel cell is expected as a power source for, e.g., a fuel cell vehicle.
In order to increase the utility factor of hydrogen (fuel gas), the hydrogen discharged from the fuel cell is recycled by using an ejector, for example. However, when moisture (water vapor) discharged from the fuel cell together with the hydrogen is circulated, the fuel cell tends to come into a moisture excessive state. In view of such a situation, a catch tank is disposed in a piping line for circulating anode off-gas to prevent return of the moisture discharged from the fuel cell to the fuel cell again.
Japanese Unexamined Patent Application Publication No. 2007-059221 discloses a technique of detecting a level of water produced and stored in a gas-liquid separator (catch tank), estimating, based on the detected water level, a volume of moisture refluxed from the gas-liquid separator to the fuel cell, and discharging the water produced and stored in the gas-liquid separator when the estimated volume of the refluxed moisture exceeds a predetermined value.
Japanese Unexamined Patent Application Publication No. 2007-123040 discloses a technique of, after turning-off of an ignition switch, removing liquid droplets in an oxidant-gas flow passage and liquid droplets in a fuel-gas flow passage at different timings to suppress the driving of an air compressor, thereby reducing noise.